Method and device for transferring data wherein a bit rate adaptation model is signaled between the transmitter and the receiver

ABSTRACT

The invention relates to a method for enabling most reliable packet orientated data transfer to take place by using an ARQ-method, especially a hybrid-ARQ-method, preferably for use in a mobile radio system. The invention also relates to a bit rate adaptation model which is used for signaling between the transmitter and the receiver.

This application is based on and hereby claims priority to PCTApplication No. PCT/DE02/04745 filed on Dec. 27, 2002.

BACKGROUND

The present disclosure relates to a method and corresponding apparatusfor transferring data according to an ARQ method, especially a hybridARQ method, in a communication system, such as a mobile radio system,for example

The use of so-called “packet-access methods” or “packet-oriented dataconnections” is often recommended especially in connection with mobileradio systems, since the message types produced often have a very highburst factor with the result that only short periods of activity exist,interrupted by long breaks. Packet-oriented data connections may, inthis case, considerably increase efficiency compared to other datatransfer methods in which a continuous data stream is. This is becausein data transfer methods with a continuous data stream, once a resourcehas been allocated, such as, for example, a carrier frequency or a timeslot, it remains allocated during the entire communication relationship(i.e., a resource remains occupied even if there are momentarily no datatransfers taking place, which means that this resource is not availablefor other network users). The result is that the narrow frequency rangeavailable for mobile radio systems is not used to the best effect.

Future mobile radio systems, such as, those that comply with the mobileradio standard UMTS (Universal Mobile Telecommunications System), forexample, will offer a multitude of different services whereby multimediaapplications will become increasingly prevalent alongside pure voicetransmission. The diversity of services associated with this, withdifferent transmission rates, requires a highly flexible access protocolon the air interface of future mobile radio systems. Packet-orienteddata transmission systems have proved to be highly suitable in thiscontext.

In connection with UMTS mobile radio systems, a so-called ARQ (AutomaticRepeat Request) method has been proposed in packet-oriented dataconnections. In this method the data packets transferred from atransmitter to a receiver are checked for quality at the receiving endfollowing decoding. If a data packet is erroneous on receipt, thereceiver requests retransmission of this data packet by the transmitter(i.e., a repeat data packet that is identical or partially identical tothe one previously sent and which was erroneous on receipt, is sent fromthe transmitter to the receiver (the terms full or partial repeat areused to indicate whether the quantity of data contained in the repeatdata packet is less than or equal to that of the original data packet)).With regard to this ARQ method proposed for the UMTS mobile radiostandard, which is also known as a hybrid ARQ method, the intention isfor both data and so-called header information to be transmitted in adata packet, whereby the header information also contains informationfor error checking, (e.g., CRC (Cyclic Redundancy Check) bits), and canalso be coded for error correction (known as FEC, Forward ErrorCorrection).

In accordance with the current status of UMTS standardization, it isproposed that the bits in the individual data packets and/or repeat datapackets be transferred following execution of a corresponding channelcoding by means of QAM modulation (quadrature amplitude modulation). Inthis procedure the individual bits are mapped, via a process known as“gray mapping”, onto corresponding QAM symbols which form atwo-dimensional symbol area. This is problematic, since, in the proposedQAM modulation with alphabetic scope, which includes more than four QAMsymbols, the reliability of the bits to be transferred variesconsiderably between the higher-value bits and the lower value bits.This is particularly disadvantageous with regard to the channel codingthat is to be carried out, -since, for this-purpose, it is preferable touse turbocoders which require the reliability of the bits to remainconsistent in order to achieve a sufficiently high level of efficiency.In a hybrid ARQ method, in which the repeat data packet is identical tothe original data packet, the result of the aforementioned feature ofvariable bit reliability is that certain bits of the data packet andrepeat data packet are to be found at the same place in the QAM symbolarea, thus reducing the efficiency of the entire data transfer andlimiting the data throughput at an early stage.

In order to resolve this problem it has previously been proposed thatthose bits which occur in the same place in the original data packet andin the repeat data packets be mapped to different QAM symbols in the QAMsymbol area by dynamic rearrangement of the “gray mapping”.

This will be explained in greater detail below with reference to FIGS.4A-4D. FIG. 4A shows the signal constellation/QAM symbol area for a16-QAM modulation, in which bits i₁ and i2 as well as q₁ and q₂ aremapped to a corresponding QAM symbol 26 of the two-dimensional QAMsymbol area 25 in the sequence i₁ q₁ i₂ q₂. Each of the columns/rows ofQAM symbol 26 in the two-dimensional QAM symbol area 25 that can be usedfor each bit i₁, i₂, q₂, q₂ is marked with a line. Thus, for example,the bit i₁=“1” can only be mapped onto QAM symbols in the first twocolumns of the QAM symbol area. Thanks to “gray mapping” the reliabilityof the higher-value bit i₁ is greater than the reliability of the lowervalue bit i₂. In addition, the bit reliability of the bit i₂ fluctuatesdepending on the corresponding QAM symbol 26 transferred (i.e.,depending on whether the corresponding QAM symbol 26 is arranged in theouter left or outer right column of the QAM symbol area 25). The sameapplies for bits q₁ and q₂, since bits q₁ and q2 are mapped in a mannerequivalent to the mapping of bits i₁ and i₂ (albeit orthogonally forthis purpose).

According to the conventional methods explained on the basis of FIGS.4A-4D, it has been proposed that a different “gray mapping” be used forrepeat data packets than the one used for the original data packets.Thus, for example, the “gray mapping” illustrated in FIG. 4B can be usedfor a first repeat data packet, while a “gray mapping” as shown in FIG.4C is used for a second repeat data packet, and a “gray mapping” asshown in FIG. 4D can be used for a third repeat data packet. Comparisonof FIGS. 4A-4D clearly shows that different QAM symbols 26, i.e.,different points in the two-dimensional QAM symbol area 25, are mappedto one and the same bit combination i₁ q₁ i₂ q₂. This dynamic variationof the “gray mapping” may, for example, continue to the extent that,after a certain number of repeats, each bit i₁, i₂, q₁ and q₂ istransferred to a place in the QAM symbol area 25 with excellent or goodreliability or poor reliability, whereby this procedure can be optimizedfor a different number of repeats.

It may be seen from FIGS. 4A-4D that this procedure is relatively costlysince the “gray mapping” process must be modified for each repeat datapacket.

SUMMARY

The present disclosure proposes a method and a corresponding apparatusfor transferring data according to an ARQ method, in which the problemexplained above (i.e., that of achieving reliable data transfer withhigh data throughput) may be resolved by simple means.

The presently disclosed methods and apparatus are, in particular, basedon the concept of signaling and/or transferring the bit rate adaptationmodel to be used for bit rate adaptation (e.g., the parameters requiredfor calculating this bit rate adaptation model) between a transmitterand receiver in order to retrieve the transferred information with goodquality at the receiving end.

Depending on the disclosed examples, the signaling of the bit rateadaptation model or the transfer of the parameters required in order tocalculate this bit rate adaptation model is carried out from thetransmitter to the receiver or vice versa.

In particular, one bit may be provided for this signaling of the bitrate adaptation model, and this bit, for example, may be transferredwith the corresponding data packet or as part of the corresponding datapacket, and indicates whether the data packet is a self-decoding or anon-self-decoding data packet depending on whether this bit is occupiedby a “1” or a “0”, for example.

Assuming an optimum channel is used, self-decoding data packets containso many systematic bits that the data packet can be decoded at thereceiving end solely on the basis of the bits in the data packet. Inparticular, a self-decoding data packet may contain all systematic bits.

The disclosed method and apparatus are also based on the finding that,if bits are repeated (at least some of the bits in the data packet aretransferred within the data packet more than once), all systematic bitsare always transferred and, therefore, the data packet is alwaysself-decoding. Thus, in this case any signaling as to whether the datapacket is self-decoding or non-self-decoding is superfluous and thetransmission resource provided for this purpose, such as, for example,the aforementioned bit, may be used for other purposes. In particular,this transmission resource may be used for signaling of bit rateadaptation models to be used for bit rate adaptation, especially fortransferring the parameters required for calculating these bit rateadaptation models. As a result it may be possible, where bits arerepeated, to signal a greater number of different rate adaptation modelsfor self-decoding data packets than if bits are punctured.

In general the disclosed method and apparatus achieve data transferaccording to an ARQ process to become more flexible and the transferresources available to be used more effectively.

A development of the disclosed method and apparatus is based on theconcept of applying different rate adaptation models, i.e., differentpuncturing or repetition models, to the individual bits of the originaldata packet and of the individual repeat data packets, so that bits withan identical information source (i.e., all bits with an identicalinformation source) are transferred from the transmitter to the receiverafter bit rate adaptation has been carried out in different places inthe data packet and in the repeat data packet.

As a result, the corresponding bits become located at different placesin each data packet even before the QAM modulation is carried out, andare, thus, mapped to different points or QAM symbols in the QAM symbolarea without modification of the “gray mapping”.

Moving the rate adaptation model between the originally transmitted datapacket on the one hand to the subsequent repeat data packet or packetson the other, means that one and the same code rate is obtained. It alsomeans, however, that the transmission quality and the bit error rate canbe improved. In this way an even distribution of reliability in the bitsto be transferred between the data packets and the subsequent repeatdata packets is achieved, so that an efficient channel coding procedure,for example using turbo-coders, can be carried out, the overall resultbeing that a sufficiently high level of efficiency in information ordata transfer is achieved while at the same time a high data throughputis guaranteed.

If several repeat data packets are requested it is advantageous to usewhichever rate adaptation model was applied (i.e., the appropriatepuncturing/repetition model is applied) being moved from repeat datapacket to repeat data packet).

In a further example, a rate adaptation algorithm known per se isprovided for the purpose of bit rate adaptation, whereby an offset valueused according to this rate adaptation algorithm, and which essentiallydetermines the rate adaptation model to be used in each case, variesbetween the original data packet and the repeat data packet or betweenthe individual repeat data packets. The variation of this offset valuemay enable a more efficient coding to be achieved than in a conventionalhybrid ARQ method.

The channel-coded bit stream may preferably be separated into severalparallel partial bit streams (in a process known as bit separation) forthis purpose, whereby rate adaptation models that are independent of oneanother, i.e., with independent puncturing or repetition of bits, areapplied to the individual partial bit streams, so that, once thecorresponding bits of this partial bit stream have finally been combined(in a process known as bit collection), the required bit rate adaptationcan be achieved, with the different offset value, with regard to theoriginal data packet and the individual repeat data packets. Theseparation of the bit stream into several parallel partial bit streamsenables a particularly high degree of flexibility to be achieved inchannel coding.

Since the corresponding receiver of the data packets or repeat datapackets thus processed ought to know which offset value was used, andsince any explicit transfer of this offset value may be disadvantageous,the offset value may, for example, be modified synchronously with thecorresponding time slot and/or with the corresponding frame, so that thereceiver may infer the offset value used in each case directly from thetime slot and/or frame received. In a different embodiment of theinvention, this offset value is to be signaled between the transmitterand the receiver.

In the bit separation process explained above, involving the separationof the bits into several parallel partial bit streams, in the final bitcollection the different parallel partial bit streams may also becombined with one another proportionately for each data packet or repeatdata packet, whereby this process may be used to particularlyadvantageous effect if bit repetition is applied. The offset valueexplained above may be adjusted for the original data packet and theindividual repeat data packets such that the moving together of theresulting rate adaptation models is maximized and/or as many as possibleof the matching bits in the original data packet or the correspondingrepeat data packet are mapped onto different points in thetwo-dimensional symbol area during the final modulation.

The method described above functions optimally if the bits are mappedonto the required modulation symbol area immediately after rateadaptation has been carried out. However, this is not always the casesince a process called interleaving, whereby the bits arechronologically rearranged, often takes place between rate adaptationand modulation. In a random interleaver, neighboring bits would bedistributed randomly to the corresponding points or symbols in thetwo-dimensional symbol area, so that movement by one bit, which can beachieved by varying the offset value as described above, would alsoresult in a random modification of the points or symbols of thetwo-dimensional symbol area. However, this would not be ideal since itis best for the allocation to be modified such that a bit that is lessreliable during transmission of the original data packet is mapped, in arepeat data packet to be transferred subsequently, to a position withhigher reliability in the modulation symbol area (e.g., the QAM symbolarea) and vice versa, while in a random rearrangement, onlyapproximately 50% of the maximum potential gain might be achieved.

For this reason it is preferable for a highly regular interleaver,(e.g., a block interleaver) to be used for interleaving. Additionally,the number of columns to which the interleaver distributes the bits,with subsequent column rearrangement or column permutation, and thenumber of points or symbols of the symbol area used that are differentlyweighted or have different levels of reliability, should be coprime, sothat optimum mapping is achieved.

This variation of the disclosed methods and apparatus is considerablyfar less complex compared to the known method explained previously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for clarifying signal processing according to adisclosed packet-oriented ARQ method.

FIG. 2 is a diagram for clarifying the communication in a mobile radiosystem.

FIG. 3 shows a rate adaptation algorithm, that may be used in thedisclosed examples for the purpose of rate adaptation.

FIGS. 4A-4D are diagrams for clarifying the mapping of bits from anoriginally transmitted data packet or from corresponding repeat datapackets to QAM symbols.

DETAILED DESCRIPTION OF THE PRESENT EXAMPLES

As already explained, the following is based on the idea thatpacket-oriented data transfer in a mobile radio system, as shownschematically in FIG. 2 for example, is to be implemented with the helpof the disclosed methods and apparatus. Thus, for example, FIG. 2 showsthe communication between a base station 1 and a mobile station 2 of amobile radio system, such as a UMTS mobile radio system, for example.The transfer of information from the base station 1 to the mobilestation 2 takes place via the so-called downlink channel DL, while thetransfer of information from the mobile station 2 to the base station 1takes place via the so-called uplink channel UL.

The disclosed methods and apparatus are explained below using as anexample a packet-oriented data transfer from the base station 1 to themobile station 2, i.e., a packet-oriented data transfer via the downlinkchannel, in which the disclosed method and apparatus can also be usedsimilarly on data transfer via the uplink channel. These methods andapparatus are further explained below on the basis of the signalprocessing measures to be executed in the transmitter concerned. Howeverit is noted that a corresponding signal processing operation in thereverse sequence is required in the relevant receiver for evaluation ofthe data processed in this way at the transmitter end, which means thatnot only the transmitter end is affected, but also the receiver end.

FIG. 1 shows the signal processing of the data and header information tobe transferred in data packets following a exemplary hybrid ARQ method.

On the header side, header information created by a function block 3 issupplied to a function block 12, which ensures that all headers of alldata packets that are to be transmitted in the same radio packet arelinked together into a single header (in a process known as headerconcatenation). A function block 13 inserts CRC bits for headerdetection into the resulting header information. The resulting bitstream is then subjected to channel coding by a function block 14 andrate adaptation by a function block 15. An interleaver, 16, causes thesymbols and/or bits supplied to it to be arranged in a particular wayand time-interleaved. The data blocks produced by the interleaver 16 areallocated by a function block 17 to the individual transmit or radioframes (known as radio frame segmentation).

A function block 4 is also provided on the data side for the insertionof CRC bits. A function block 5 is used for splitting the data suppliedto a channel coder 6 such that a coding process limited to a specificnumber of bits can always be carried out by the channel coder 6.

Because of the channel coding carried out by the channel coder 6, theactual data to be transmitted has redundant information inserted in it.Systematic bits and parity bits are systematically produced by thechannel coder, whereby each systematic bit is identical to aninformation bit and parity bits are redundant bits that are determinedfrom the information bits. In an ARQ method, consecutively transmitteddata packets contain bits with the same information source, i.e., bitsthat each depend on the same information bit.

The bits produced by the channel coder 6 are supplied to a functionblock 19, which adjusts the bit rate of the bit stream by masking oromitting individual bits (known as puncturing) or repeating individualbits. So-called DTX (Discontinuous Transmission) bits can be insertedinto the data stream by a subsequent function block 9. Also provided onthe data side are function blocks 10 and 11, which perform the samefunctions as do function blocks 16 and 17 on the header side.

Finally the bits produced on the data and header side are mapped ormultiplexed by a function block 18 on whatever physical transfer ortransmission channel is available at the time and transferred to thereceiver with the help of a suitable modulation procedure, such as QAMmodulation, for example.

In the hybrid ARQ method, if a data packet is incorrectly received ordecoded by the receiver, a repeat data packet is requested. The repeatdata packet is identical or partially identical to the previously sentand incorrectly received packet (HARQ type I, Chase Combining). Thelatter methods are known as partial incremental redundancy (IR) or asHARQ type III. As a further option the repeat packets may also consistpurely of additional redundant information known as parity bits (full IRor HARQ type II).

The terms full or partial repeat are used to indicate whether thequantity of data contained in the repeat data packet is less than orequal to that of the original data packet. The data packet and thecorresponding repeat data packet have at least some bits with the sameinformation source. Therefore, by evaluating the data packet originallysent together with the subsequent repeat data packets requested, thereceiver can retrieve the originally transmitted information with betterquality.

The function section 19 includes a function block 20, which, dependentupon control exercised by the function block 3, separates the coded bitsproduced by the upstream channel coder 6 into at least two parallelpartial bit streams, which are each subjected to rate adaptationseparately (i.e., independently of one another). In this regard FIG. 1shows three partial bit streams A-C, each of which has one functionblock 21-23 provided for rate adaptation as appropriate (i.e., forpuncturing or repetition of individual bits). This results in severaldifferently coded parallel partial bit streams, which are supplied to afurther function block 24. This further function block 24 has the taskof bit collection (i.e., collecting the individual bits from theparallel bit streams in the same sequence that was used by functionblock 20 for the bit separation process, such as the separation into theindividual parallel partial bit streams). This is to ensure that thesequence of bits remaining after rate adaptation remains unchangedoverall.

As already explained, the rate adaptation processes provided for theindividual partial bit streams A-C by function blocks 21-23 may takeplace completely independently of one another. In particular, it is alsopossible for the bits from one or more bit streams not to be subjectedto any puncturing or repetition at all. In general the rate adaptationprocess for the individual parallel partial bit streams A-C should beselected such that a required rate adaptation model is applied by theentire function section 19 to the channel-coded bit stream produced byfunction block 6 for each data packet or repeat data packet. Byimplementing function section 19 with several rate adaptations inparallel as shown in FIG. 1, extremely high flexibility can be achievedin the coding process.

The function section 19 is designed such that, according to the controlexercised by the function block 3, it applies a different rateadaptation model to the bits of a repeat data packet than to the bits inthe corresponding, originally transmitted, data packet. This means thatfunction section 19 is notified by function block 3 as to whether arepeat data packet has been requested by the corresponding receiver,whereby function section 19 in this case selects and/or adjusts the rateadaptation model implemented by the individual function blocks 21-23,such that the bits of the repeat data packet are processed overall witha different rate adaptation model than the bits of the basic data packetthat was originally transmitted.

The rate adaptation process implemented overall by the function section19 may, for example, be carried out according to the rate adjustmentalgorithm shown in FIG. 3, which is already known in the conventionalart.

For example, a rate matching (i.e., rate adaptation) algorithm containedin the UMTS standard is described in ”Multiplexing and Channel Coding(FDD) Release 1999, “Technical Specification 3GPP TS 25.212. Thealgorithm uses the following as the main parameters:

-   -   x_(b): number of coded bits per packet in bit stream b    -   e_(ini): starting error value (NTTI/3)    -   e_(plus): increment in the error value during        puncturing/repetition    -   e_(minus): decrement in the error value per output bit.

In the existing standard (e.g., for the downlink of turbocoded transportchannels with fixed bit position (See, e.g., Chapter 4.2.7.2.1 of theabove cited UMTS Standard), these parameters are to be calculated asfollows in cases of puncturing:e_(ini)=N_(max)  (5.1)where N_(max) refers to the maximum number of bits per parity bit streamvia all transport formats and transport channels, calculated before rateadaptation. The increments and decrements in the error values arecalculated as follows:e _(plus) =α×N _(max) , e _(minus) =α×|ΔN _(i) ^(b)|  (5.2),where a=2 for the first parity bit stream and a=1 for the second paritybit stream. |ΔN_(i) ^(b)| is the number of punctured bits per bit streamb for the transport channel i.

In particular, a rate adaptation parameter e_(ini) is used whichindicates an offset value with regard to the rate adaptation model usedfor each rate adaptation carried out. An error variable e is initializedwith this offset value e_(ini) at the beginning of the rate adaptationalgorithm shown in FIG. 3, whereby the error e indicates for example theratio between the current puncturing rate and the required puncturingrate in the case of puncturing.

Finally the index m of the bits currently to be processed is set to thefirst (i.e., to the value 1) and an auxiliary error parameter eplus isinitialized. A loop is then run for all bits in the data packet No. i tobe processed, whereby the number of bits for the data packet in questionis indicated by x_(i).

Within this loop, first the error e is repeated and checked using afurther auxiliary error parameter e_(minus), to ascertain whether theresulting error e is greater than zero, in order to determine whether ornot the corresponding bit is to be punctured. If the above condition isfulfilled, the corresponding bit is set to an auxiliary value δ and ispunctured (i.e., blocked for the subsequent data transfer). If, however,the above condition is not fulfilled, the corresponding bit is selectedfor the data transfer and the error e is calculated again using thefirst auxiliary error parameter mentioned above, namely, e_(plus).

At the conclusion of the rate adaptation algorithm or puncturingalgorithm, the bit index m is incremented and, thus, the next bit isselected for processing as explained above.

The rate adaptation model applied to the bits in a data packet or repeatdata packet can essentially be affected by appropriate selection of theoffset value e_(ini). By varying this offset value e_(ini) it ispossible for a different rate adaptation model to be applied to a repeatdata packet than was applied to the corresponding, originallytransmitted, data packet, whereby the rate adaptation may be applied inparticular with reference to the parity bits of the individual partialbit streams A-C (compare FIG. 1).

The offset value e_(ini) is selected for the originally transmitted datapacket and the repeat data packet, such that the moving together of theresulting rate adaptation models is maximized. Furthermore the offsetvalue e_(ini) for the originally transmitted data packet and the repeatdata packet is to be advantageously selected so that during the finalmodulation, in particular the QAM modulation, as many of the matchingbits in the two packets as possible are mapped onto different points(i.e., different QAM symbols), of the corresponding two-dimensional QAMsymbol area (compare in this regard the mappings shown in FIG. 4, forexample).

A self-decoding data packet is normally used for the first transfer,(i.e., all systematic bits are transferred, for example). If, once thesesystematic bits are subtracted, there is only sufficient space remainingin the transfer for some of the parity bits, the parity bits arepunctured accordingly (i.e., not transferred). However, if the availablespace is greater than all existing parity bits, then systematic bits andparity bits are repeated with the same rate. The selection ofpunctured/repeated bits takes place in UMTS by means of an algorithmwhich distributes these punctured/repeated bits as evenly as possiblewithin the coded data block.

In a repeat data transfer, the rate adaptation model and, thus, the bitsto be transferred in each case, are selected on the basis of a specificnumber of signaling bits, such that, firstly, different HARQ types areimplemented, and, secondly, the bits transferred in each transfer are asdifferent as possible, in order to achieve a decoding gain and/or evendistribution of the total energy to all bits. A specific rate adjustmentmodel or the parameters for calculating a specific rate adaptation modelhere correspond to a specific redundancy version. A variant of thisshows how the selection of redundancy versions can be optimized for agiven number of bits for signaling of the various redundancy versions,both in the case of puncturing, and also in the case of repetition, inparticular.

To enable the receiver to interpret the received data packet correctly,a signal is sent between the transmitter and the receiver to indicatewhether the data packet is a self-decoding or a non-self-decoding datapacket. Bit signaling information is required for this purpose. Withineither type (self-decoding or a non-self-decoding), further redundancyversions can then be defined, which can likewise be explicitly signaled.If n bits are available for signaling, then the total amount ofinformation to be signaled consists of one bit for differentiatingbetween self-decoding and non-self-decoding, and n−1 bits for describinga specific redundancy version from a multitude of redundancy versions.

Use of Signaling bits

Self-decoding data packet 1 bit Redundancy version n − 1 bits

However, differentiation between self-decoding and non-self-decodingdata packets is worthwhile only in the case of puncturing, in which notall coded bits can be transferred. In the case of repetition,self-decoding exists, a priori, since all coded bits can indeed betransferred several or even many times over. In the case of repetition,therefore, it is advantageous to use all n bits in order todifferentiate between different redundancy versions. Particularly in thecase of repetition, even where n is a small number, this makes itpossible to ensure, with far greater certainty, that the power isdistributed as evenly as possible over all transferred bits after arepeat data packet is transferred and the first data packet is overlaidwith the repeat data packet at the receiving end. An exemplaryembodiment of the use of the signaling bits according to the inventionis shown in the following table:

Use of Signaling Bits in Puncturing and Repetition

Puncturing Repetition Self-decoding data packet 1 bit 0 bits Redundancyversion n − 1 bits n bits

For example, the value n=3 might be selected here. This permits areasonable number of different redundancy versions and, furthermore,does not require an unnecessarily high number of signaling bits.

The method presented here optimizes the signaling process since thesignificance of the signaling bits depends on whether bits are repeatedor punctured in the transfer in question. If a total of Ng signalingwords is provided (i.e., Ng=2n where n bits are provided for signaling),then the Ng signaling words are distributed as follows.

In the case of puncturing, the signaling words are divided into twopartial quantities; one for transfers of the self-decoding type (i.e.,systematic bits are included); and a second for transfers of thenon-self-decoding type (systematic bits are not usually included, and inparticular, systematic bits are not included). Within these partialquantities, then, different signaling words differentiate betweendifferent redundancy versions.

Ns redundancy versions of the self-decoding type (e.g., PartialIncremental Redundancy) are selected, which indicate self-decodingredundancy versions, and Ng-Ns redundancy versions of thenon-self-decoding type (Full Incremental Redundancy) are provided. IfNs=Ng/2, the coding already provided is used. Another extreme case isNs=1. In this case, only a single self-decoding redundancy version isprovided (which is provided for the initial transfer) and Ng−1non-self-decoding redundancy versions. This is the best choice where Ngis relatively small (maximum 8), since it still enables a relativelyhigh number of redundancy versions with full IR to be defined.

In the case of repetition, no partial quantities are formed and allsignaling words are used to differentiate between various redundancyversions.

The main innovations in this exemplary embodiment are thedifferentiation of cases of repetition and puncturing for thesignificance of the signaling bits and the optimization of the number ofpossible HARQ types and different redundancy versions, -and, in the caseof repetition as well as for-puncturing, with a specified number ofsignaling bits. Different redundancy versions may be generated accordingto a parameter variation of the parameter e_(ini), but may also begenerated according to any other procedure.

Until now, the only parameters that have been described are those thatinfluence the rate adaptation or the bit selection for an HARQ system,and the way in which such parameters can be signaled. In fact, however,it is by varying other parameters that improvements in the transfer rateare achieved. An example of such a parameter is the variation in themapping of bits to 16 QAM symbols in the stage for mapping modulationsymbols. The principle of this method is described in the followingstandardization documents, by way of example:

R1-01-0237, Panasonic,“Enhanced HARQ Method with Signal ConstellationRearrangement, “3GPP TSG RAN WG1, Las Vegas, USA, Feb. 27-Mar. 2, 2001;and R1-01-1059, Pasonomic, “Comparison of HARQ Schemes for 16-QAM, “3GPPTSG RAN WG1, Sophia Antipolis, France, Nov. 5-7, 2001; R1-01-0151,Panasonic, “16-QAM F+HARQ Bitmapping Scheme”, Espoo, Finland, January,2002.

This method essentially achieves good results if the same redundancyversion is used in repetition (chase combining) or if the redundancyversions differ only slightly in terms of their bit content. Incontrast, incremental redundancy achieves the best results if theindividual redundancy versions transmitted differ greatly. Ideally,therefore, the signaling should be designed such that differentredundancy versions as well as different mapping variants are used forbitmapping to 16 QAM symbols. However, this is not always possiblebecause of the limited availability of signaling bits. In this case itis necessary to decide whether the signaling bits are used for selectingredundancy versions or selecting mapping variants. Embodiments for theseexemplary variants are explained below. In an initial exemplaryembodiment with reference to this aspect, no mapping variants—butexclusively redundancy versions—are signaled if the modulation type usedis not 16 QAM or 8 PSK, or a higher-value modulation, but only BPSK,QPSK, or a different modulation type which does not have differentvalues for modulation symbols.

In a further exemplary embodiment, for example if a 16 QAM modulation isused, it is preferable for mapping variants to be signaled—if necessaryat the expense of redundancy versions—if so many bits are available fortransfer that all the bits present can be transferred, in other words ifpuncturing does not need to be used for rate adaptation.

In a further exemplary embodiment, it is preferable for mapping variantsto be signaled (if necessary at the expense of redundancy versions), iffewer bits are available for transfer, so that not all the bits presentcan be transferred, in other words puncturing must be used for rateadaptation if the puncturing rate, i.e. the proportion of bits to bepunctured, does not exceed a certain predefined value. In principle thispredefined value may be selected at random, but it is better if it isnot lower than 50%, since, with 50% puncturing by selection of twocompletely orthogonal (i.e. disjunct) redundancy versions, an excellentimprovement can be achieved through incremental redundancy. Otherwise itis not possible, in this case, to achieve any additional gain throughmapping variations, since the two transfers do not contain any commonbits in which a gain might be produced. In this case, therefore, it isnot absolutely necessary to signal mapping variations in addition toredundancy versions.

In a further exemplary embodiment, the aforementioned exemplaryembodiments may be expanded such that there is no firm switching to andfrom between signaling formats depending on the parameters describedabove, but that more or fewer redundancy versions or mapping variantsare signaled according to parameter. There follows an example of a casein which a total of four alternatives might be signaled:

-   -   If the puncturing rate is more than 50%, all four alternatives        are used for the signaling of redundancy versions and no mapping        variants are signaled.    -   If the puncturing rate is between 50% and 33%, 3 alternatives        are used for the signaling of redundancy versions and one        alternative is signaled for a mapping variant (which can then        only be used for a special redundancy version).    -   If the puncturing rate is between 33% and 20%, two alternatives        (i.e. one bit) are used for the signaling of redundancy versions        and likewise two alternatives (i.e. one bit) are signaled for        two mapping variants. This enables the redundancy version and        mapping variant to be selected independently of one another.    -   If the puncturing rate is between 20% and 10%, an alternative is        used for signaling a redundancy version (which can then only be        used for a special mapping version), and three alternatives are        used for mapping variants.    -   If the puncturing rate is less than 10% with repetition up to        33%, all four alternatives are used for the signaling of mapping        variants and no redundancy versions are signaled.    -   If the repetition rate is over 33%, then two alternatives (i.e.        one bit) are again used in each case for the signaling of        redundancy versions and mapping variants. This enables the        redundancy version and mapping variant to be selected        independently of one another.

In the above exemplary embodiments the ratio of bits available fortransfer to bits present, and the resulting puncturing or repetitionrate, has been used as a criterion. It is necessary to point out that,even though this puncturing rate may well be the puncturing rate thatresults from the ratio of number of bits after channel coding to numberof bits that are transferred, there may be cases in which furtherinterim stages are carried out. For example, puncturing may be carriedout first on an interim number of bits that corresponds to the size of areceiving memory, and it is only from this number that puncturing orrepetition is carried out on the number of bits to be transferred. Inthis case the criterion would preferably be the puncturingrate/repetition rate in this second stage, not the overall rate.

According to another example, an interleaver is used for the functionblock 10 shown in FIG. 1, which does not interleave randomly but in ahighly regular manner. A block interleaver, for example, might be usedfor function block 10. If the interleaver used as function block 10 is ahighly regular interleaver, and if the number of columns to which theinterleaver distributes the bits supplied to it and the number ofdifferently weighted points in the two-dimensional QAM symbol area orthe number of differently weighted modulation points in general, arecoprime, the result is optimum mapping. According to the current stateof UMTS standardization, the proposed interleaver is a block interleaverwith additional column replacement, which distributes neighboring bitsto columns separated from one another in multiples of “5”, and thenexchanges the columns. For example, if 30 columns are used the columnpermutation is as follows: column no. 0, 20, 10, 5, 15, 25, 3, 13, 23,8, etc. Since the value “5” is coprime with the number of differentbits, for example in a 16-QAM modulation (i.e., two bits) and a 64-QAMmodulation (i.e., three bits), then this combination, for example,results in good scrambling or mapping to the corresponding modulationpoints.

This method as described above is possible for both puncturing andrepetition, as well as for the most diverse transport formats. Byappropriately selecting the parameters (e.g. number of redundancyversions, number of bit streams), it can be adapted to differentmodulation and coding schemes.

It should be understood that various changes and modifications to thepresently preferred examples described herein will be apparent to thoseskilled in the art. Such changes and modifications can be made withoutdeparting from the spirit and scope of the present invention. It istherefore intended that such changes and modifications be covered by theappended claims.

1. A method for transferring data according to an ARQ methodologycomprising: transferring data is transferred from a transmitter to areceiver in the form of data packets wherein at least one repeat datapacket is transferred by the transmitter to the receiver aftertransmission of a data packet when a corresponding request is issued bythe receiver, and the bits to be transferred in the data packet and atleast one repeat data packet are subjected to bit rate adaptation beforethey are transferred from the transmitter to the receiver; utilizing oneor more bit rate adaptation models for bit rate adaptation, includingusing parameters of the one or more bit rate adaptation models forcalculation of the bit rate adaptation; and signaling at least one ofthe one or more bit rate adaptation models from the transmitter to thereceiver for use in differentiating between self-decoding andnon-self-decoding data packets.
 2. A method as defined in claim 1,wherein the differentiation according to self-decoding andnon-self-decoding data packets is signaled only in the case ofpuncturing, but not in the case of repetition.
 3. A method as defined inclaim 1, wherein at least two different bit rate adaptation models aresignaled.
 4. A method as defined in claim 1, wherein a total number ofpossible signaled bit rate adaptation models for self-decoding ornon-self-decoding data packets in the case of puncturing is the same asthe number in the case of repetition.
 5. A method as defined in claim 1,wherein for cases of puncturing, one bit is provided for indicating aself-decoding or non-self-decoding data packet and n−1 bits are providedfor indicating different bit rate adaptation models, and, in cases ofrepetition, n bits are provided for indicating different bit rateadaptation models.
 6. A method as defined in claim 1, wherein two bitsare provided in cases of puncturing, and three bits are provided incases of repetition to indicate different bit rate adaptation models. 7.A method as defined in claim 1, wherein different bit rate adaptationmodels are used for bit rate adaptation of the data packet and therepeat data packet, so that bits with an identical information sourceare transferred from the transmitter to the receiver after bit rateadaptation is carried out at different places in the data packet and inthe repeat data packet.
 8. A method as defined in claim 1, furthercomprising: dividing the bits of a channel-coded bit stream into two ormore partial bit streams; subjecting each individual partial bit streamto a separate bit rate adaptation process for the purpose of bit rateadaptation; and recombining the bits of the individual partial bitstreams with one another after the corresponding bit rate adaptation forthe data packet or repeat data packet has been carried out.
 9. A methodas defined in claim 8, further comprising: combining the bits of theindividual partial bit streams with one another proportionately afterthe corresponding bit rate adaptation for the data packet or repeat datapacket has been carried out.
 10. A method as defined in claim 1, whereinthe bit rate adaptation model used for the repeat data packet ismodified compared to the bit rate adaptation model used for the datapacket, in that when a QAM modulation of the bits to be transferred iscarried out, bits with identical information content are mapped withregard to the repeat data packet onto different points in the QAM signalarea than for the originally transmitted data packet.
 11. A method asdefined in claim 1, wherein bit rate adaptation is carried out with theaid of a bit rate adaptation algorithm, which punctures or repeats thebits of the data packet or repeat data packet depending on the value ofa corresponding rate adaptation parameter (e_(ini)), whereby the valueof the rate adaptation parameter (e_(ini)) is modified for the bit rateadaptation of the bits in the repeat data packet compared to the bitrate adaptation of the bits in the data packet.
 12. A method as definedin claim 11, wherein the bit rate adaptation algorithm is configuredsuch that it selects the bits to be punctured or repeated using an errorvariable (e), whereby said error variable (e) is initialized with thevalue of the rate adaptation parameter (e_(ini)) at the start of therate adaptation algorithm.
 13. A method as defined in claim 1, whereindifferent bit rate adaptation models are used when several repeat datapackets are requested by the receiver for bit rate adaptation of thebits in the individual repeat data packets.
 14. A method fortransferring data according to an ARQ methodology comprising:transferring data from a transmitter to a receiver in the form of datapackets, wherein at least one repeat data packet is transferred to thereceiver by the transmitter after transmission of a data packet when acorresponding request is issued by the receiver; subjecting bits to betransferred in the data packet or the at least one repeat data packet tobit rate adaptation by puncturing or repetition before they aretransferred from the transmitter to the receiver, wherein the bit rateadaptation is carried out according to a bit rate adaptation model; andsignaling the bit rate adaptation model, including parameters forcalculating the bit rate adaptation model, from the transmitter to thereceiver, wherein a signal is sent from the transmitter to the receiverto indicate whether the data packet is self-decoding ornon-self-decoding when bit rate adaptation is accomplished bypuncturing.
 15. A method as defined in claim 14, wherein no signal issent from the transmitter to the receiver to indicate whether a datapacket is self-decoding or non-self-decoding when the bit rateadaptation is accomplished by repetition.
 16. A method as defined inclaim 14, wherein a transmission resource used in the case of puncturingin order to signal whether a self-decoding or non-self-decoding datapacket is being transferred, is alternately used in the case of bit rateadaptation accomplished by repetition to signal from the transmitter tothe receiver the bit rate adaptation model, including parameters forcalculating the bit rate adaptation model.
 17. A method as defined inclaim 14, wherein at least two different bit rate adaptation models aresignaled.
 18. A method as defined in claim 14, wherein a total number ofpossible signaled bit rate adaptation models for self-decoding ornon-self-decoding data packets in the case of puncturing is the same asthe number in the case of repetition.
 19. A method as defined in claim14, wherein for cases of puncturing, one bit is provided for indicatinga self-decoding or non-self-decoding data packet and n−1 bits areprovided for indicating different bit rate adaptation models, and, incases of repetition, n bits are provided for indicating different bitrate adaptation models.
 20. A method as defined in claim 14, wherein twobits are provided in cases of puncturing, and three bits are provided incases of repetition to indicate different bit rate adaptation models.21. A method as defined in claim 14, wherein different bit rateadaptation models are used for bit rate adaptation of the data packetand the repeat data packet, so that bits with an identical informationsource are transferred from the transmitter to the receiver after bitrate adaptation is carried out at different places in the data packetand in the repeat data packet.
 22. A method as defined in claim 14,further comprising: dividing the bits of a channel-coded bit stream intotwo or more partial bit streams; subjecting each individual partial bitstream to a separate bit rate adaptation process for the purpose of bitrate adaptation; and recombining the bits of the individual partial bitstreams with one another after the corresponding bit rate adaptation forthe data packet or repeat data packet has been carried out.
 23. A methodas defined in claim 14, further comprising: combining the bits of theindividual partial bit streams with one another proportionately afterthe corresponding bit rate adaptation for the data packet or repeat datapacket has been carried out.
 24. A method as defined in claim 14,wherein the bit rate adaptation model used for the repeat data packet ismodified compared to the bit rate adaptation model used for the datapacket, in that when a QAM modulation of the bits to be transferred iscarried out, bits with identical information content are mapped withregard to the repeat data packet onto different points in the QAM signalarea than for the originally transmitted data packet.
 25. A method asdefined in claim 14, wherein bit rate adaptation is carried out with theaid of a bit rate adaptation algorithm, which punctures or repeats thebits of the data packet or repeat data packet depending on the value ofa corresponding rate adaptation parameter (e_(ini)), whereby the valueof the rate adaptation parameter (e_(ini)) is modified for the bit rateadaptation of the bits in the repeat data packet compared to the bitrate adaptation of the bits in the data packet.
 26. A method as definedin claim 25, wherein the bit rate adaptation algorithm is configuredsuch that it selects the bits to be punctured or repeated using an errorvariable (e), whereby said error variable (e) is initialized with thevalue of the rate adaptation parameter (e_(ini)) at the start of therate adaptation algorithm.
 27. A method as defined in claim 14, whereindifferent bit rate adaptation models are used when several repeat datapackets are requested by the receiver for bit rate adaptation of thebits in the individual repeat data packets.
 28. An apparatus to transferdata according to an ARQ method comprising: a transmitter configured totransfer data to a receiver in the form of data packets, wherein thetransmitter is configured such that, after transmission of a datapacket, the transmitter transfers a repeat data packet to the receiverwhen a corresponding request has been received from the receiver; and abit rate adaptation unit configured to apply bit rate adaptation to bitsto be transferred in the data packet or repeat data packet by thetransmitter, including that bit rate adaptation models to be used forbit rate adaptation, including parameters required for calculation ofthe bit rate adaptation, and effect signaling from the transmitter tothe receiver in order to effect a distinction between self-decoding andnon-self-decoding data packets.
 29. An apparatus as defined in claim 28,wherein the bit rate adaptation is further configured to effectsignaling of at least two different bit rate adaptation models.
 30. Anapparatus as defined in claim 28, wherein the distinction according toself-decoding and non-self-decoding data packets is signaled only in thecase of puncturing, and not in the case of repetition.
 31. An apparatusas defined in claim 28, wherein different bit rate adaptation models areused for bit rate adaptation of the bits in the repeat data packet andfor bit rate adaptation of the bits in the data packet, so that bitswith an identical information source are transferred by the transmitterto the receiver after bit rate adaptation is carried out at differentplaces in the data packet and repeat data packet.
 32. An apparatus asdefined in claim 28, wherein the bit rate adaptation unit comprises: abit separation unit configured to separate the bits in a channel-codedbit stream into at least two partial bit streams; at least two bit rateadaptation units allocated to the individual partial bit streams inorder to subject the individual partial bit streams to separate bit rateadaptation processes; and a bit collection unit configured to combinethe bits from the individual partial bit streams produced by the bitrate adaptation units.
 33. An apparatus to transfer data according to anARQ method comprising: a transmitter configured to transfer data to areceiver in the form of data packets, the transmitter configured suchthat, after transmission of a data packet, a repeat data packet istransferred to the receiver when a corresponding request has beenreceived from the receiver and bits to be transferred in the data packetor repeat data packet are subjected to bit rate adaptation by puncturingor repetition, before they are transferred by the transmitter to thereceiver; wherein the transmitter is further configured to perform thebit rate adaptation according to a bit rate adaptation model, such thatthe bit rate adaptation model, including parameters for calculation ofthe bit rate adaptation model, is signaled from the transmitter to thereceiver, and, in the case of bit rate adaptation by puncturing, asignal is sent by the transmitter to the receiver to indicate whether aself-decoding or non-self-decoding data packet is being transferred. 34.An apparatus as defined in claim 33, wherein, in the case of bit rateadaptation by repetition, no signal is sent by the transmitter toindicate whether a self-decoding or non-self-decoding data packet isbeing transferred.
 35. An apparatus as defined in claim 33, wherein atransmission resource that is used in the case of puncturing to signalwhether a self-decoding or non-self-decoding data packet is beingtransferred, is used by the transmitter, in the case of repetition, tosignal the bit rate adaptation model, including parameters forcalculating the bit rate adaptation model.
 36. An apparatus as definedin claim 33, wherein different bit rate adaptation models are used forbit rate adaptation of the bits in the repeat data packet and for bitrate adaptation of the bits in the data packet, so that bits with anidentical information source are transferred by the transmitter to thereceiver after bit rate adaptation is carried out at different places inthe data packet and repeat data packet.
 37. An apparatus as defined inclaim 33, wherein the bit rate adaptation unit comprises: a bitseparation unit configured to separate the bits in a channel-coded bitstream into at least two partial bit streams; at least two bit rateadaptation units allocated to the individual partial bit streams inorder to subject the individual partial bit streams to separate bit rateadaptation processes; and a bit collection unit configured to combinethe bits from the individual partial bit streams produced by the bitrate adaptation units.
 38. A method as defined in claim 1, furthercomprising the steps of receiving and evaluating a data packet or repeatdata packet at a receiver in order to determine the information contentof the data packet by evaluating together the bits received in the datapacket and in the repeat data packet.
 39. A method for transferring dataaccording to an ARQ methodology comprising: transferring data from atransmitter to a receiver in the form of data packets, wherein at leastone repeat data packet is transferred to the receiver by the transmitterafter transmission of a data packet when a corresponding request isissued by the receiver; subjecting bits to be transferred in the datapacket or the at least one repeat data packet to bit rate adaptation bypuncturing or repetition before they are transferred from thetransmitter to the receiver, wherein the bit rate adaptation is carriedout according to a bit rate adaptation model; and signaling the bit rateadaptation model, including parameters for calculating the bit rateadaptation model, from the transmitter to the receiver, wherein a signalis sent from the transmitter to the receiver to indicate whether thedata packet is self-decoding or non-self-decoding when bit rateadaptation is accomplished by puncturing; wherein the data packet istransferred according to a QPSK modulation or a higher-value modulation,including one of a 16-QAM modulation and 8-PSK modulation, wherein amapping rule for the mapping of bits in the data packet to modulationsymbols including parameters for describing the mapping rule is signaledfrom the transmitter to the receiver only in the case of a higher-valuemodulation, whereby signaling resources are used for this purpose, whichare used in the case of QPSK modulation for signaling the bit rateadaptation model including parameters for calculating the bit rateadaptation model.